docs: def store_rlzs_by_grp(dstore):
      """
      Save in the datastore a composite array with fields (grp_id, gsim_id, rlzs)
      """
      lst = []
      assoc = dstore['csm_info'].get_rlzs_assoc()
      for grp, arr in assoc.by_grp().items():
          for gsim_id, rlzs in enumerate(arr):
              lst.append((int(grp[4:]), gsim_id, rlzs))
      dstore['csm_info/rlzs_by_grp'] = numpy.array(lst, rlzs_by_grp_dt)